Subject: [PATCH] ACPI/IORT: Fix PCI ACS enablement

From: [email-masked] (Zhou Wang)
Date: Sat, 23 Sep 2017 10:26:29 +0800

On 2017/9/22 17:45, Lorenzo Pieralisi wrote:
> On Thu, Sep 21, 2017 at 07:32:58PM +0800, Zhou Wang wrote:
>> On 2017/9/20 1:05, Lorenzo Pieralisi wrote:
>>> commit f6810c15cf97 ("iommu/arm-smmu: Clean up early-probing
>>> workarounds") removed kernel code that was allowing to initialize
>>> and probe the SMMU devices early (ie earlier than PCI devices through
>>> linker script callback entries) in the boot process because it was not
>>> needed any longer in that the SMMU devices/drivers now support deferred
>>> probing.
>>>
>>> Since the SMMUs probe routines are also in charge of requesting global
>>> PCI ACS kernel enablement, commit f6810c15cf97 ("iommu/arm-smmu: Clean
>>> up early-probing workarounds") also postponed PCI ACS enablement to
>>> SMMUs devices probe time, which may be too late given that PCI devices
>>> needs to detect if PCI ACS is enabled to init the respective capability
>>> through the following call path:
>>>
>>> pci_device_add()
>>>  -> pci_init_capabilities()
>>>   -> pci_enable_acs()
>>>
>>> Add code in the ACPI IORT SMMU platform devices initialization path
>>> (that is called before ACPI PCI enumeration) to detect if an SMMU is
>>> present in HW and enable PCI ACS if it actually is, restoring the
>>> correct PCI ACS enablement sequencing.
>>>
>>> Fixes: f6810c15cf97 ("iommu/arm-smmu: Clean up early-probing
>>> Signed-workarounds")
>>> Signed-off-by: Lorenzo Pieralisi <[email-masked]>
>>> Cc: Will Deacon <[email-masked]>
>>> Cc: Robin Murphy <[email-masked]>
>>> Cc: Zhou Wang <[email-masked]>
>>> Cc: Alex Williamson <[email-masked]>
>>> ---
>>>  drivers/acpi/arm64/iort.c | 11 +++++++++++
>>>  1 file changed, 11 insertions(+)
>>>
>>> diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c
>>> index 9565d57..71a7694 100644
>>> --- a/drivers/acpi/arm64/iort.c
>>> +++ b/drivers/acpi/arm64/iort.c
>>> @@ -1184,6 +1184,7 @@ static void __init iort_init_platform_devices(void)
>>>  	struct acpi_table_iort *iort;
>>>  	struct fwnode_handle *fwnode;
>>>  	int i, ret;
>>> +	bool smmu_detected = false;
>>>  
>>>  	/*
>>>  	 * iort_table and iort both point to the start of IORT table, but
>>> @@ -1218,11 +1219,21 @@ static void __init iort_init_platform_devices(void)
>>>  				acpi_free_fwnode_static(fwnode);
>>>  				return;
>>>  			}
>>> +
>>> +			smmu_detected = true;
>>>  		}
>>>  
>>>  		iort_node = ACPI_ADD_PTR(struct acpi_iort_node, iort_node,
>>>  					 iort_node->length);
>>>  	}
>>> +
>>> +	/*
>>> +	 * If IORT reports an SMMU component make sure PCI ACS is
>>> +	 * requested so that PCI devices can enable it in their
>>> +	 * capabilities.
>>> +	 */
>>> +	if (smmu_detected)
>>> +		pci_request_acs();
>>>  }
>>>  
>>>  void __init acpi_iort_init(void)
>>>
>>
>> Hi Lorenzo,
>>
>> I tested this patch, it works well in my HiSilicon Hip08 based system.
>> However, setting ACS flag at the stage of SMMU device init seems not good,
>> I mean what if in one system there are only platform devices connected to
>> SMMU device.
> 
> That's a fair point if you explain to me how current pci_request_acs()
> usage copes with your remark above.

The current pci_request_acs usage for ARM SMMU-V3 sets ACS flags under CONFIG_PCI.
However, as mentioned in your commit message, this setting is too late.

For the usage of X86 and AMD, as I am not familiar with the devices used in these
two platforms, maybe the default devices in these platforms are PCIe based :)

Best,
Zhou

> Lorenzo
> .